This invention relates to an infrared microscope. More particularly, this invention relates to a mechanism including an aperture for an infrared microscope for limiting its field of view, or a surface area of a sample to be measured.
An infrared microscope is used to analyze a sample, exposed to an infrared light beam, based on the spectrum (or the intensity distribution according to the wavelength) of the reflected infrared light from the surface of the sample or the transmitted infrared light which has been transmitted through the sample. In such an analysis by using an infrared microscope, the size of the area which can be captured at once in its field of view is usually very small, being on the order of 100 .mu.m-1 mm. At times, however, an analysis is carried out over even a smaller part of this already small area, for example, when attention is to be focused on a small impurity material which has been discovered within the field of view. Thus, an infrared microscope is usually provided with a mechanism including aperture plates or the like for limiting its field of view such that an analysis over a very small area or on a very small object on the surface of a sample can be carried out. Such a mechanism serves to limit the field of view appropriately such that only the light reflected from or transmitted through a reduced target area or object can be detected while the noise due to infrared light received from areas other than the target area can be cut and hence that a spectral analysis with high accuracy can be achieved.
A mechanism for limiting the field of view of an infrared microscope usually includes a plurality of planar members (herein referred to as "the aperture plates") for together forming an aperture for allowing only a part of infrared light received from a sample to pass therethrough and a driving mechanism for adjusting the positions and orientations of these aperture plates so as to conveniently change the shape and the size of the aperture. The driving mechanism serves to transmit the motion of a power source through screws and gears to the aperture plates as well as other components. The power source may be of a manual type requiring the user, say, to rotate a handle, or of an electrical type comprising pulse motors or linear motors.
FIGS. 4A and 4B show a portion of a prior art infrared microscope including its aperture-forming part 32, an optical system 34 and a sample stage 36, FIG. 4A being a partially sectional frontal (horizontal) view and FIG. 4B being a sectional plan view taken along line 4B--4B of FIG. 4A. Although not shown in FIGS. 4A and 4B, the sample stage 36 is provided with its own driving mechanism and can be thereby moved not only within a two-dimensional plane defined by the X-axis and the Y-axis but also in the direction of the height along the Z-axis shown in FIGS. 4A and 4B. The optical system 34 includes lenses and the like (not individually shown) and is disposed directly above the sample stage 36, and the aperture-forming part 32 is disposed directly above this optical system 34 such that its central axis coincides with the central axis 33 of the optical system 34.
The aperture-forming part 32 includes four aperture plates 40, 41, 42 and 43 and their holder 38 which is supported by the main body (not shown) of the infrared microscope so as to be rotatable around the aforementioned central axis 33. Of the four aperture plates 40, 41, 42 and 43, the plates 40 and 42 form a mutually opposite pair adapted to move slidingly along a straight line (along the X-axis), and the plates 41 and 43 form another mutually opposite pair adapted to move slidingly along another straight line (along the Y-axis) which is perpendicular to the direction of sliding motion of the plates 40 and 42. The driver for the aperture-forming part 32 is usually adapted to cause these pairs of aperture plates (40 with 42 and 41 with 43) to move in synchronism with each other and by same distances in mutually opposite directions.
When such an infrared microscope is used for the analysis of a sample, the sample is first placed as indicated by numeral 44 on the sample table 36 below the optical system 34 and a visible light source 46 is switched on. The position of the sample stage 36 along the Z-axis is adjusted until an enlarged image 45 of the sample 44 is formed on the focusing plane of the aperture-forming part 32 (that is, the contact surface between the upper and lower ones of the aperture plates 40, 41, 42 and 43). While observing this enlarged image 45 through an optical system for this purpose (not shown), the user operates the driver (not shown) for the aperture-forming part 32 to appropriately change the positions of the aperture plates 40, 41, 42 and 43 as well as the angle of rotation of the holder 38 and the position of the sample stage 36 within the X-Y plane such that unwanted portions of the enlarged image 45 of the sample 44 will be excluded from the open area of the aperture 48. After this adjustment is done, the visible light source 46 is switched off and an infrared light source 47 is switched on to carry out a spectral analysis of the infrared light reflected by the sample 44.
Most aperture-forming parts for an infrared microscope use four aperture plates with a straight edge to form a rectangular aperture, as shown in FIG. 4B. In such a case, the user adjusts the aperture usually in the following steps although they may not be carried out in the same sequence.
Firstly, the user operates the driver for the sample stage 36 in order to appropriately change the position of the sample stage 36 within the X-Y plane until the relative position (X, Y) of the aperture with respect to the sample is determined. Secondly, the user operates the driver for the aperture-forming part 32 in order to appropriately modify the angular position of the holder for the aperture plates with respect to the main body of the infrared microscope until the relative angular position of the aperture with respect to the sample is determined. Thirdly, the user operates the same driver to appropriately change the separations d1 and d2 (as shown in FIG. 4B) between the mutually opposite pairs of the aperture plates 40 with 42 and 41 with 43 until the lengths of the edges of the rectangular aperture are determined.
When these steps are carried out with a prior art infrared microscope of a typical kind, the user is required to set the position of the sample stage by operating switches for moving the X-axis and the Y-axis, to set the angular position of the holder by rotating a handle for the purpose and to operate on handles for varying the separations d1 and d2. In summary, these operations had to be carried out individually one at a time. If the size of the aperture is made smaller than that of the sample with a prior art infrared microscope of the type shown in FIGS. 4A and 4B, however, it becomes impossible to visually ascertain the whole image of a sample and hence the user had to be extremely careful in order to match the aperture with a target area for the measurement on the surface of the sample. If the user is inexperienced, in particular, the adjustment of aperture takes an unreasonably long time, and this affects the overall work efficiency of the analysis.
In view of the above, Japanese Patent Application 8-140952 described a new infrared microscope adapted to display a sample image taken by a photographing means on a screen of a display device, to generate a virtual image of an aperture on the basis of a signal corresponding to the actual opening of the aperture, and to display it superposed on the aforementioned sample image such that the user can easily ascertain on the display screen to which area on the sample surface the aperture corresponds.